Chemistry

What is in an atom?

Central nucleus surrounded by one or more shells of electrons. The nucleus consists of two particles: protons & neutrons.

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Charges in the nuclus

PROTON: mass=1, charge=1 NEUTRON: mass=1, charge=0 ELECTRON: mass= negligable, charge= -1

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Atomic number and mass number

Number of protons/electrons: ATOMIC NUMBER (underneath) Number of neutrons is MASS NUMBER-ATOMIC NUMBER

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Describe an Isotope?

No two element have the same number of protons and the number of neutrons in the nucleus is not fixed. Some atoms of the same element have different neutrons hence different MASS numbers- THESE DIFFERENT FORMS OF THE SAME ELEMENT ARE CALLED ISOTOPES.

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What is the reletive atomic mass? Ar

Scientists express the mass of an atom relative to the mass of the carbon atom 12C. As 12 is its mass number the mass of another atom is compared wiith 1/12 of the mass of carbon.

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What is the relative molecular mass? Mr

Can be calculated by adding together the relative atomic masses of the atoms that make it up. It is know as the 'relative formula mass' when talking about ionic compounds.

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Describe the electronic structure?

Electrons in an atom are at different energy levels-shells. The first shell can contain 2 electrons and the 2,3 can contain up to 8 electrons. ELECTRON CONFIGURATION is an alternatice term for the electronic structure.

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How can the electron structure be worked out by the periodic table?

The GROUP number gives the number of electrons in the outer shell. (Exception Group 0-full). The PERIOD indicates how many shells of electrons the atom has.

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What are the ALKALI metals?

Reactive metals in Group 1.

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Describe ALKALI reactions with OXYGEN

Alkali metals are soft, shiney metals that react immediately on contact with oxygen in the air - they tarnish, or corrode, forming a layer of the metal oxide on the surface.They need to be stored under oil.REACTIONS BECOME MORE VIOLENT DOWN THE GROUP

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Describe ALKALI reactions with WATER

They react very vigorously with water. Lithium fizzes on contact, forming lithiym hydroxide and bubbles of hydrogen gas. REACTIONS BECOME MORE VIOLENT DOWN THE GROUP. Na reacts so hot that it ignites hydrogen and creates a lilac flame.

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Describe ALKALI reactions with HALOGENS (Elements in group 7)

Form salts. MORE VIOLENT DOWN THE GROUP. The reactions of the alkali metals with oxygen with water and with halogens shows us that the reactivity of the alkali metals increase DOWN the group.

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Alkali metals present in compounds such as lithium chloride, sodium bromide or potassium sulfate can be identified by heating a sample in a roaring Bunsen Burner flame and noting the colour observed. What colours should we expect for each compound?

Lithium compounds: red flame ..... Sodium compounds produce a yellow-orange flame..... Potassium compounds produce a lila coloured flame.

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Halogen 'Fluorine' reaction with iron wool

Cold iron wool bursts into flame as fluorine gas flows over it: Iron(III) fluoride, FeF3 is the product.

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Halogen 'Chlorine' reaction with iron wool

Hot iron woll glows brightly when chlorine gas flows over it: Iron (III) chloride, FeCl3 is the product.

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Halogen 'Bromine' reaction with iron wool

Hot iron wool glowsm but less brightly, when bromine vapour flows over it: Iron (III) bromide, FeBr3 is the product.

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Halogen 'Iodine' reaction with iron wool

Hot iron wool shows a faint red glow when iodine vapour flows over it; Iron (III) iodide, Fel3 is the product.

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In summary describe halogen reactions with iron

THE HALOGENS GET PROGRESSIVELY LESS REACTIVE DOWN THE GROUP. Fluorine is such a reactive gas that it cannot be used in schools.

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What is Displacement reactions?

A MORE reactive HALOGEN can DISPLACE a LESS reactive HALOGEN from a SOLUTION OF ITS SALT. e.g chlorine, the second most reactive halogen, will displace both bromine and iodine from solutions of bromides and iodides.

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What is the silver nitrate test?

HALODE IONS can be identified by their reactions with silver nitrate. Chloride, Bromide and Iodide ions in solution with the silver ions in silver nitrate to form insoluble percipitates of: WHITE- silv chloride CREAM-silv bromide YELLOW-silv iodide

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What is Metallic bonds?

[2 METALS] All solid metals have a structure consisting of a LATTICE (regular repeating structure) of fixed positive ion in a sea of free moving electrons creating METALLIC BONDS. They need to lose electrons to form positive ions.

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The lattice/free moving electrons explain the physical properties of Metallic bonds.. How is the electrical conductivity affected?

It is a good electrical conductor of metals: Because the sea of free moving electrons carry negatie charges, so the electrical current (flow of charge) can pass easily through the structure when voltage is applied.

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The lattice/free moving electrons explain the physical properties of Metallic bonds.. How is the thermal conductivity affected?

The positive ions are close together/bonded strongly by the metallic bonds. The structure can easily pass the vibration of hot ions from one ion to another.Also the free moving electrons can move faster when heated so can change heat from hot to cold

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Describe Ionic Bonding?

When a metal reacts with a nonmetal they TRANSFER ions to become neutral (+ and - ions cancel out) If they gain= -1 If they lose= +1 . + charges are attracted to - charges (electrostatic attraction)so ions are held in a 3 dimentional lattice strongly

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The ionic lattice model explains the physical properties of ionic bonding.. How is the high melting points of ionic compounds affected?

The positive and negative ions have very strong attractive electrostatic forces between them, which need a lot of energy (from heating) to overcome them.

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The ionic lattice model explains the physical properties of ionic bonding.. How is the electrical conductivity (none) of ionic compounds affected?

The postive and negative ions are held in FIXED positions within their lattice and are not free to move. As there are no moving charged particles, there will be no electrocal conduction.

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The ionic lattice model explains the physical properties of ionic bonding.. How is the electrical conductivity (yes) of ionic compounds affected?

When dissolved or molten in water, ionic compouns do conduct electricity. The lattice breaks down on melting or dissolving, and the ions are free to move and create an electrical current.

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The ionic lattice model explains the physical properties of ionic bonding.. How is the brittleness of ionic substances affected?

If a stress force is applied to an ionic solid (a crystal), this shifts the ion layers slightly and the layers will tend to jump over eachother. Ions of the same charge are then brought side by side so repel against eachother-The crystal fractures.

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What are Simple Molecular Bonding (Covalent Bonds) ?

[2 NONMETALS] SHARE electrons to form neutral molecules. They need to GAIN electrons to form a full outter shell. Some atoms can form DOUBLE COVALENT BONDS where each atom share four electrons (in two pairs). Occurs in C02.

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Explain the physical properties of Simple Molecular Bonds (Covalent Bonds)

Covalent bonds between atoms in a molecule are very strong. Only very weak forces exist between different molecules-each molecule is electriaclly neutral. Solid covalent sunbstances have low melting points as little energy is needed to turn sol 2 liq

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What are Giant covalent structures? Two examples?

Diamond and graphite consist of carbon atoms and are GIANT covalent structures. They have high melting points because all the atoms are held together by strong covalent bonds. Carbon has 4 outer electrons;needs to share 4 electrons for full outer.

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Describe the covalent bonds in carbon

Each carbon atom is connected to four other carbon atoms by strong covalent bonds, forming a tetrahedral-shaped structure.

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Describe the covalent bonds in graphite

Layers of carbon atoms are arranged in hexagonal rings.Each carbon atom forms strong covalent bonds with THREE others in the same layer. The FOURTH electron from each atom joins a mobile system of electrons between the layers.Weak bond between layers

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Explain the physical properties in diamond

All four electrons in outer shell are involved in covbonding and a rigid giant cov structure of carbon is formed. Gives diamond extreame hardness and high melting point as a lot of energy is required to break down the lattice.No free elects-no electr

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Explain the physical properties in graphite

Weak bonds between the layers so has a slippery feel and good lubricating properties. The strong covalent bonds within the layers mean that the melting point is high. The mobile electrons allow graphite to conduct electricity well ALONG the layers

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What are Carbon nanotubes?

another physical form of carbon. They are molecular-scale tubes of rolled up GRAPHITE layers about 10,000 times thinner than a human hair. They are stiffer/stronger than steel and are electrical

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Explain the physical properties of carbon nanotubes

The covalently bonded hexagonal cerbon sheets make carbon nanotubes incredibly strong. The free moving electrons give them a higher electrical conductivity than copper.

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What are smart materials?

Smart materials have properties which change reversibly with a change in their surroundings.

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What are pigments used in?

Paints and dyes

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What are THERMOCHROMIC PIGMENTS?

Change colour at specific temperatures. Their uses include: mugs that change colour with hot liquids, battery power indicators, T shirts change colour on body temperature.

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What are PHOTOCHROMIC PIGMENTS?

They change colour with light intensity. Their uses include: T-shirt design, Photochromic (self-darkening) lenses in glasses.

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What are Shape-memory Polymers?

Are plastics (polymers) that, after deformation, can regain their original shape when they are heated. This property is called Shape Retentation?

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What are Shape-memory polymer uses?

Sealing around window frames, sportswear such as helmets and GUM SHIELDS.

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What are Shape-memory alloys?

They are metal alloys that regain their original shape when heated.

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What are Shape-memory alloy uses?

Surgical plats for joining bone fractures, surgical wires for replacing tendons, thermostats for electrical devices, deformable spectacle frames.

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What are hydrogels?

They are polymers that can ABSORB or EXPELL water and SWELL or SHRINK up to 1000 times their volume). Small changes in the stimulus-either TEMP or PH - control the amount of swelling/shrinking.

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What are hydrogels used for?

Underground water cut-off in the oil industry (the volume of gel is pH controlled). Artifical muscles (hydrogels can be more effective than shape memory alloys). Buildings threatened by forest fires (they're more effective than fire fighting foam).

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What is a rate of reaction?

How much product (usually by mass/volume) is produced in a set time (usually per second).

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How does a graph show the rate of reaction?

It allows us to determine the rate of reation - the gradient (slope) of the graph tells us how much product is being produced per unit time.

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Measuring rates of reaction: MEASURING THE VOLUME OF GAS PRODUCED experiment....

This can be done by displacing water from a graduated tube or by collecting the gas directly using a gas syringe. The volume of gas produced will increase with time, up to a maximum volume. This graph goes up to a constant rate.

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Measuring rates of reaction: MEASURING THE AMOUNT OF LIGHT PASSING THROUGH experiment..

Some reactions produce a solid PRECIPITATE. If light is shone through the reaction as more and more precipitate forms the light intensity passing through will decrease. The can be measured using light sensors. The graph will go down to a constant.

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Measuring rates of reaction: MEASURING THE CHANGE IN MASS experiment..

An electronic balance can be used to measure the overall mass of a reaction. If gas is produced as one of the reactions products then the overall mass will decrease with time as gas ESCAPES. The graph will go down to a constant rate.

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Explain when a chemical reaction occurs?

When the reacting particles collide with one another. Not all collisions result in a chemical reaction: the collision needs enough ENERGY for the BONDS in the reactant molecules to BREAK!

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Explain the rate of reaction and how it is increased?(successful..)

The number of SUCCESSFUL collisions is a small % compared to how many collisions are actually taking place. The higher the collision frequency, the higher the rate of reaction.

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What is the number of successful collisions called per second?

The collision frequency.

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Factors affecting the rate of chemical change are...

Temperature, Concentration and Surface area of reactants.

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Factors affecting the rate of chemical change: DESCRIBE THE TEMPERATURE OF THE REACTANTS?

A higher temperature means a higher rate of reaction. This is because FASTER the particles means that MORE collisions will take place increasing the chances of collision frequency meaning higher rate of reaction!

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Factors affecting the rate of chemical change: DESCRIBE THE CONCENTRATION OF THE REACTANTS?

A higher concentration means a higher rate of reaction becuase it increases the TOTAL number of reacting particles in the SAME volume. More particles per unit volume mean more collisions are likely increasing chance of collision frequency-higher rofr

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Factors affecting the rate of chemical change: DESCRIBE THE SURFACE AREA OF THE REACTANTS?

A higher surface area means a higher rate of reaction because increasing the surface area allows more of the reactants to COLLIDE with eachother with enough energy. As more collisions are caused the higher % of collision frequency will go-higher rofe

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What does a Catalyst do?

Increases the rate of reaction but remain chemically unchanged at the end of the reaction.

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How does a Catalyst work?

It provides a 'surface' on which the reacting molecules can collide with eachother - this REDUCES the amount of energy needed for a COLLISION to be successful. Increasing the rate of collision frequency hence rate of reaction.

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Why are Catalysts used for?

They are used in the production of bulk and fine chemicals, petrochemicals and in food processing: 90% of all commercial chemical products involve catalysts at some stage in their manufacture.

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Why are Catalysts important?

They reduce the amount of energy required to produce chemical products. This therefore preserves world fuel reserves and reduces the environment impact of burning fossil fuels - global warming.

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What is the crude oil extracted from oil wells a mixture of? Describe what they are?

HYDROCARBONS: Compounds that only contain carbon and hydrogen.

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What is fractional distillation?

Separating crude oil into less complex mixtures known as fractions.

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What is the boiling point for hydrocarbons in crude oil?

DIFFERNT! It is this property that is used to separate them. The LONGER the carbon chaiin in the MOLECULE the HIGHER the boiling point.

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What is an atom?

.Atom is smallest unit which consisit of proton, neutron and surrounded by electron. No of proton is always equal to no of electron and thus atom is no charge.

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What is a molecule?

Molecule is combination of atoms with bond. Molecule is created by bonded atoms when electrons fill up the outer orbit of each atom.

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Describe the first 3 steps of the process of fractional distillation?

1.Crude oil is heated as it enters the FD column (fractionating column) 2.When the temperature is at boiling point for some of the hydrocarbons they will begin to evaporate from the oil. 3.Vapour will cool as it rises in column away from the heat

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Describe the last 2 steps of the process of fractional distillation?

4.When vapour cools below its BP it will CONDENSE 5.The hydocarbs with bigger molecules have higher BP so will not rise so far before condensing. The point where they condense, the HC can be collected-each fraction has different collecting point

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Why bother with fractional distilation?

Crude oil is a naturally occuring substance in the earths crust and it is a mixture of hydrocarbons. You can separate them into fractions (useful substances) by FD. Each fraction has a diffferent boiling point and that is why FD works. Each Fraction

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What happens to the fractures after fractional distillation?

They get treated after collecting to remove impurites.

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What happens to fractions with low boiling points when the enter the fractionating column?

They rise to the top as they have small molecules hence smaller boiling points. They then cool down, condense and form a liquid into that fraction.

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What happens to fractions with high boiling points when the enter the fractionating column?

As they have longer chained molecules they have higher boiling points meaning they will not rise as far in the column and will condense at a different collecting point.

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What property does crude oil go in as? What property are the hydrocarbons? What property are the fractions after condensing?

Liquid ---> Gas ---> Liquid

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What is the importance of the different boiling points in fractional distilation?

Different boiling points create different fractions which can then be used to create different substances e.g. Gasoline for Petrol, Petroleum gases for Heaters.

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What happens to the hydrocarbons with such low boiling points?

They do not get cold enough to condense and are therefore collected as a gas at the top of the column (petroleum gases)

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What happens to the hydrocarbons with such high boiling points?

They do not evaporate! They are 'Left over' as residue and are collected from the bottom of the column.

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What happens to the hydrocarbons that have similar boiling points?

The process cannot separate each one so the fractions collected are still mixtures.

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Go and practice some PERCENTAGE COMPOSITION OF SIMPLE COMPOUNDS.

TOTL RELATIVE MASS OF ELEMENT/TOTAL MASS (MR) x100

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Go and practice some MASS ES OF REACTANTS AND PRODUCTS.

1) Write down equation 2)Write down what question info 3)Find Mrs 4)Change to what you need and what you do to one you do to the other (DIVIDE BY Mr AND TIMES BY INFO TOLD) ..trying to get to 1

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Go and practice some PERCENTAGE YIELD QUESTIONS.

Find Mr for before and after... PERCENTAGE YIELD=ACTUAL YIELD/THEORETICAL YIELD x100%

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Go and practice some CALCULATING ENERGY CHANGES.

1) Draw bonds under equatoin (eg H-H) 2)Calculate the energy change when BONDS in reactants break-left (POSITIVE) 3)Calculate the energy change when products form-right(energy is being realeased so MINUS) 4)MINUS - from + = kJ/Mol

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Go and practice some FINDING CHEMICAL FORMULAS (RATIOS)

[1)Find missing element grams by minusing the one side from the total] 2)Divide grams by each elements atomic mass-Mr 3)Divide these numbers by smallest Mr answer 4)Ratio them 5)Sub ratios into formula

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What is cracking?

Fractions from crude oil undergo it- long molecule chains are heated in the presence of a catalyst to make shorter/useful fractions (petrol).

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Describe what happens to the molecules during cracking?

They split into TWO! The one product is used for a different fraction and the other product is not complete as it is broken so it links itself together via a DOUBLE bond- this is an ALKENE. This can be used as a MONOMER-make plastic

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Alkanes and Alkenes are different types of...

HYDROCARBONS!

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What are ALKANES?

SATURATED hydrocarbons! Their molecules contain SINGLE BONDS only which means they are 'saturated' with hydrogen (they contain as much hydrogen as possible- in their structual formula each carbon is bonded to 4 other atoms-no more atoms can be added)

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What are ALKENES?

UNSATURATED hydrocarbons! This is because of the double bond (if the double bond opened up two more atoms could be added) They can be used as a monomer to make plastics. The double bond makes them more reactive than alkane.

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What are addition reactions?

UNSATURATED ALKENES take part in this due to their carbon to carbon double bond as it means other atoms(hydro and bromine)can be added to the molecule by removing one of the double lines and adding necessary lines so that carbon is still bonded to 4

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What are addition reactions? (continued)

..molecules to complete its structure.

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What happens when HYDROGEN is added to an ALKENE? And what is this process called?

HYDROGENATION- Hydrogen added turns an alkene(Ethene)into an alkane(Ethane) This reaction happens by HEATING the alkene in the presence of a CATALYST.

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What happens when BROMINE is added to an ALKENE? And what is this process called?

DIBROMOALKANE-The double bond in the alkenes break and attach two bromine atoms. It is a useful reaction as it can be used to test the presence of an alkene: BROWN/ORANGE bromine water reacts with the alkene and its colour DISAPPEARS turns COLOURLESS

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